UTF-8、GBK等格式互相转换 [Windows/Linux 通用]

#ifdef WIN32
#include 
#endif
#ifdef OS_UNIX
#include 
#endif
#if defined(WIN32)
void convert_encoding(const char *input, int from_codepage, int to_codepage, char *output)
{
	int wlen = MultiByteToWideChar(from_codepage, 0, input, -1, NULL, 0);
	if (0 == wlen)
		return;
	wchar_t *wbuf = (wchar_t *)malloc((wlen + 1) * sizeof(wchar_t));
	MultiByteToWideChar(from_codepage, 0, input, -1, wbuf, wlen);
	int len = WideCharToMultiByte(to_codepage, 0, wbuf, -1, NULL, 0, NULL, NULL);
	if (0 == len)
	{
		free(wbuf);
		return;
	}
	WideCharToMultiByte(to_codepage, 0, wbuf, -1, output, len, NULL, NULL);
	free(wbuf);
}
#else
void convert_encoding(const char *input, const char *from_encoding, const char *to_encoding, char *output)
{
	iconv_t cd = iconv_open(to_encoding, from_encoding);
	if (cd == (iconv_t)-1)
		return;
	size_t in_len = strlen(input);
	size_t out_len = in_len * 2; // 输出长度最多为输入长度的2倍
	char *in_ptr = input, *out_ptr = output;
	size_t ret = iconv(cd, &in_ptr, &in_len, &out_ptr, &out_len);
	if (ret == (size_t)-1)
	{
		iconv_close(cd);
		return; // 转换失败
	}
	*out_ptr = '\0'; // 添加字符串结尾
	iconv_close(cd);
}
#endif
// 用法例：
// 从共享内存取到UTF-8格式的字符串res，转换为GBK格式字符串tmpstr
#ifdef WIN32
		convert_encoding(res, CP_UTF8, CP_ACP, tmpstr);
#else
		convert_encoding(res, "UTF-8", "GBK", tmpstr);
#endif